A television signal in the National TV Standards Committee (NTSC) system has a multiplexed form in which a luminance signal Y is balanced-modulated by a chroma signal C.
Therefore, a known television receiver receives a television signal, separates the television signal into a luminance signal Y and a chroma signal C (Y/C separation), and decodes the chroma signal, so as to generate component signals including a luminance signal Y, a color-difference signal R-Y, and a color difference signal B-Y. Further, the television receiver performs matrix conversion so as to generate RGB signals, and supplies the RGB signals to a display device such as a cathode ray tube (CRT). Accordingly, color video images can be displayed.
FIG. 1 shows an example of the configuration of a main part of a known television receiver.
In FIG. 1, a tuner 12 of the television receiver 1 receives a video carrier signal of a predetermined channel through an antenna 11, generates a video intermediate frequency signal based on the video carrier signal, and supplies the video intermediate frequency signal to a video intermediate frequency (VIF) circuit 13. The VIF circuit 13 decodes the supplied video intermediate frequency signal so as to generate a composite video signal, which is supplied to a Y/C separator 14.
The Y/C separator 14 separates the supplied composite video signal into a luminance signal (Y) and a chroma signal (C). Then, the Y/C separator 14 supplies the chroma signal (C) to a chroma decoder 15. The chroma decoder 15 decodes the chroma signal (C) so as to supply color-difference signals: an R-Y signal (R-Y) and a B-Y signal (B-Y), to a matrix circuit 16.
Also, the Y/C separator 14 supplies the luminance signal (Y) to the matrix circuit 16. The matrix circuit 16 generates an R signal (R), a G signal (G), and a B signal (B) based on the luminance signal (Y) supplied from the Y/C separator 14 and the R-Y signal and the B-Y signal supplied from the chroma decoder 15, and supplies the RGB signals to a CRT 17. The CRT 17 displays color video images based on the supplied R signal (R), G signal (G), and B signal (B).
In the above-described example, however, the composite video signal is separated into the luminance signal (Y) and the chroma signal (C), which is decoded so as to generate the R-Y signal and B-Y signal, and then the RGB signals are generated. In this method, the number of processes and the scale of the processing circuit become large, which is disadvantageous.
Also, when a two-dimensional or three-dimensional Y/C separator is used as the Y/C separator 14 so as to perform filter processing, image quality is often degraded, for example, dot interference or cross-color occurs at the edge of an image or in a motion picture, due to a Y/C separation error.
On the other hand, a component video signal can be directly generated from a composite video signal by using classification adaptive processing.
In this method, in order to obtain component signals, such as Y signal, R-Y signal, and B-Y signal, in a target pixel of an image corresponding to a video signal, classification is performed by using feature obtained from a composite signal of the target pixel and a pixel which is temporally or spatially approximate to the target pixel (class tap).
Then, by performing computation of a fixed coefficient prepared for each class and a predictive tap obtained from the composite signal along with the class tap, a component signal in the target pixel can be directly obtained from the composite signal.
In this case, however, when the fixed coefficient prepared for each class is not appropriate for the target pixel, degradation of image quality, such as dot interference and cross-color, cannot be adequately improved.
In order to solve this problem, a plurality of classification methods can be used and the results thereof can be combined, so as to precisely classify the feature of a composite signal and to perform adequate classification. In this case, however, the number of classes becomes numerous and thus the processing circuit for realizing this method becomes large, which is not practical.